Startup ecosystems started to emerge in different parts of the world since the 2000s. They normally focus on specific areas and present different characteristics and dynamics. Also, each ecosystem has its own path of evolution over time. In this paper, we analyze the dynamics of these ecosystems by taking the New York case study as an example. We show what stages ecosystems pass through, the requirements for each of these phases and why it is possible for many ecosystems to evolve until reaching a self-sustainable level of maturity. This research can bring a better understanding of the evolution of software startup ecosystems and what role their actors play in this development. The results can be used as a basis for ecosystem stakeholders to reflect and act concretely on improving the maturity of their local environments.